I. Field
The present invention relates generally to data communication, and more specifically to techniques for performing timer-based sleep by terminals in wireless communication systems.
II. Background
A terminal in a typical wireless communication system may only be active sporadically. For example, for packet data application, the terminal may transmit and/or receive data in short bursts and may remain in an “idle” state for significant periods of time between these data bursts However, to ensure that pertinent information can still be received by the terminal even while it is in the idle state, the terminal periodically monitors signals from the system for certain messages. These messages may include those for updating system overhead information, those for alerting the terminal to pertinent events (e.g., a hand-off), and so on.
While the terminal is in the idle state, it continues to consume power to sustain circuitry necessary to monitor the signals from the system. The terminal may be Ma portable unit (e.g., a handset) that is powered by an internal battery. In this case, power consumption by the terminal while it is in the idle state decreases the available battery resources. This would then shorten both the “standby” time between battery recharges and the “on” time for active communication. For a portable terminal, it is highly desirable to minimize power consumption in the idle state and thereby extend battery life.
In one conventional technique for reducing power consumption by a terminal in the idle state, the terminal enters a “slotted sleep” mode whereby it periodically transitions between a “sleep” state and a “monitor” state. In the sleep state, the terminal powers down as much circuitry as possible to conserve power. In the monitor state, the terminal can receive messages on an overhead channel. The overhead channel may be partitioned into numbered “paging slots” and the terminal may be assigned or designated with specific paging slots. The terminal would then enter the sleep state between successive designated paging slots, wake up prior to the next designated paging slot, monitor the overhead channel for messages, and revert to the sleep state if additional processing or communication is not required. In the time period between successive designated paging slots, the terminal is in the sleep state and the system does not send any messages specifically for the terminal. The system continues to send system overhead information, but the terminal is not required to monitor this information unless it is needed. Messages directed to this specific terminal are sent during the designated page slots for the terminal.
Conventionally, the terminal enters the slotted sleep mode if it does not have an active session with the system. While in this mode, the terminal would wake up periodically to receive messages on its designated paging slots. For some systems (e.g., CDMA systems that implement IS-2000 and IS-95), the designated paging slots for the terminal are configurable and may be negotiated between the terminal and the system. For these systems, the sleep time may be extended by assigning the terminal with paging slots that are spaced further apart in time.
However, some wireless communication systems transmit messages in designated paging slots at relatively short fixed intervals (i.e., not configurable between the terminal and the system, and relatively frequent). For example, a CDMA system that implements IS-856 (which is also referred to as an HDR system) transmits messages in paging slots that are spaced apart by 5.12 seconds. For a terminal in the idle state in such a system, the standby time for the terminal may be shortened considerably if it has to wake up at each designated paging slot. If the designated paging slots for the terminal are not configurable, then some other mechanism is needed in order to extend the sleep time for the terminal so that battery power can be conserved and standby time can be extended.
A terminal may concurrently operate on two or more systems (e.g., IS-856 and IS-2000 or IS-95) by arranging for the page slots assigned by these systems to be interleaved in a manner such that the terminal is able to process information from each system. Operating on multiple systems extends the capability of the terminal. However, for a terminal required to wake up for every designated page slot on both systems, the standby time for the terminal may shortened considerably.
There is therefore a need in the art for techniques to extend sleep time for terminals in wireless communication systems, such as those with fixed paging slots.